In a spinning mill, a spun yarn is produced by drafting a sliver with a drafting mechanism provided in a spinning frame to be a desired thickness and twisting the same with a spindle.
Fibers preferably contain a suitable amount of moisture in order to smoothly carry out the drafting operation in the drafting mechanism while suppressing the generation of flies. On the other hand, it is said that a low humidity environment is favorable for the purpose of reducing the friction between a ring and a traveller during the twisting operation so that yarn breakages are minimized due to the lowering of spinning tension.
Accordingly, it is preferable that, prior to introducing into a spinning frame room air-conditioned to be a relatively dry environment to maintain a favorable spinning condition, slivers contained in cans are stored for a predetermined period in an aging room conditioned to be a higher humidity environment relative to that of the spinning frame room and then loaded to the spinning frame to be spun into yarns. Moisture in the sliver, however, is dispersed while being placed for a long time in the spinning frame room after being loaded to the spinning frame, whereby the sliver in a dry condition is fed to the drafting mechanism and prevented from being smoothly drafted.
As one of countermeasures for solving the above problem, the present applicant proposed a system, in Japanese Patent Publication (Kokoku) No. 44-22775, in which a sliver-aging room and a spinning frame room are respectively provided upstairs and downstairs and air-conditioned independently from each other; a sliver is guided through a long tube to a drafting mechanism of a spinning frame in the downstairs spinning frame room conditioned at relatively high temperature and low humidity, from a can placed in the aging room conditioned at relatively low temperature and high humidity (hereinafter referred to as a "separation system"). According to this system, since the sliver is conveyed to the spinning frame while being tightly sealed within the tube, the sliver is prevented from losing moisture during passage.
In the separation system, air in the spinning frame room is maintained at a relatively high temperature so that the relative humidity becomes low, while air in the aging room is maintained at a relatively low temperature. In addition, air pressure in the spinning frame room is slightly lower than that in the aging room. The reason for this is that, if the pressure relationship were reversed, the high temperature air in the spinning frame room would go up the tube for guiding the sliver into the aging room where it is cooled to condense on the innerwall of tube as a dew. The dew condensation must be absolutely avoided because it obstructs the smooth advancement of sliver and results in the sliver breakage or other problems.
Therefore, according to this system, air pressure is controlled so that an air stream always generates in the tube, flowing in one direction from the upstairs aging room to the downstairs spinning frame room.
During the passage through the tube, the sliver moisture is gradually dispersed due to the descending air stream and the temperature rise to be a content (in a range of about 6.8% through 8.0% in a case of cotton) suitable for the drafting operation when the sliver reaches the drafting mechanism of the spinning frame.
The dehydration degree of the sliver in the tube varies in accordance with the change of flow rate of downward air stream in the tube; if the flow rate is more, the moisture dispersion is accelerated to cause a dry sliver; on the other hand, if the flow rate is less, the moist state is maintained. Further, the flow rate also varies in accordance with the change of sliver filling degree in the tube; if the filling degree is higher, the flow rate decreases due to the increase of flow resistance; on the other hand, if the filling degree is lower, the flow rate increases due to the reduction of flow resistance.
The filling degree in the tube corresponds to a meandering state of sliver in the tube, and should be controlled at a stage of mill design to be a predetermined value while taking the operational conditions into account, by selecting a proper material and inner diameter of tube.
If the meandering state of sliver changes as shown in FIGS. 3(a) and 3(b) in accordance with the variation of operational condition such as a sliver weight in unit length or of frictional coefficient of tube inner wall, the dehydration degree of sliver also changes, whereby the sliver of predetermined moisture content cannot be fed to the spinning frame.
An object of the present invention is to provide a simple method capable of maintaining a moisture content in sliver at a constant value even though a meandering state of sliver in a tube varies while corresponding to the variation of operational conditions.